Water-soluble cellulose ethers, particularly non-ionic cellulose ethers, are used in many fields. Of particular note is the application in ready-mixed concrete, pneumatically applied mortar or emulsion paints. In addition, the use as tablet coatings is also of importance. It is desirable to specifically match the properties of the cellulose to the particular use. The rheological properties of the cellulose ethers are particularly important in aqueous systems.
For adjusting the rheological properties, cellulose ethers are chemically modified on an industrial scale.
Hydrophobically modified cellulose ethers are one example which establish a sufficient viscosity in a narrowly limited low to medium shear range. The hydrophobic modification is carried out, by example, by reacting a cellulose ether with hexadecyl glycidyl ether. Even a few hydrophobic groups (DS <0.1) are sufficient to produce an associative interaction between the cellulose chains. The shear viscosity is thereby increased in aqueous solutions. Such hydrophobically modified cellulose ethers are used, for example, in emulsion paints. The emulsion paints can then be applied with considerably reduced spray tendency.
Also known are cellulose ethers modified with allyl groups. The modification is achieved by reacting cellulose ether with allyl glycidyl ether. Ally-modified hydroxyethyl celluloses are used industrially, for example, as protective colloids in emulsion polymerisation. A low degree of substitution of allyl groups (DS allyl) in the cellulose ether is also sufficient here to cause the desired alteration in properties (DE 19708531). The yield, based on the allyl glycidyl ether used, is generally low to moderate at ca. 15 to 40% for which reason alternatives here have also been sought.